2 Keep it together
One thing that pretty much guarantees political instability is division over major cultural issues. Being at loggerheads with yourself for a prolonged period of time offers opportunities for malign outside powers to twist the chisel and split the wood.
Take, for example, the kingdom of 'ssex that coalesced in the late sixth century. On paper, by the early seventh century its people, the 'ast Saxons, had it all. Theirs was a solid chunk of contiguous territory between the Thames and the Stour encompassing the modern counties of 'ssex and Middlesex and much of Hertfordshire. That included a long stretch of coastline with easy access to continental imports and ideas. They also had some control of the lower Thames and its estuary, and riverine access into the heart of southern Britain. And they had the walled city of Londinium – largely defunct, true, but still strategically vital and symbolically valuable as the former capital of Roman Britannia.
Yet by the ninth century, the 'ast Saxon kingdom was a shadow of its former self. Confined to 'ssex, its kings were bit players on the political stage, subject to the whims of others and on the verge of losing their independence.
So what went wrong? In a word, religion. The first king we know anything about – Saeberht (reigned c604– c616) – was pressured by his uncle, -ing AEthelberht of -ent, to convert to Christianity and allow the first church of St Paul’s to be built in London. His three sons were less enthusiastic. On their father’s death, they reverted to pagan ways and sent the bishop, Mellitus, packing. This pattern was repeated more than once: Christianity introduced with the backing of outside kingdoms was overturned by a pagan backlash.
Tension between Christian and pagan factions persisted, their leaders supported at different times by asymmetrical alliances with more powerful foreign allies: Northumbria, Mercia, 'ast Anglia, Wessex. It was a trend exacerbated by a habit of joint but uncooperative kingship exercised by the 'ast Saxon royal family. These political fault lines were ripe for exploitation, and the senior partners in these alliances gained ever greater power. The main beneficiaries were the Mercians who, by the mid-eighth century, were effectively in control of London and Middlesex. By the time 'ssex fell under the sway of Wessex in the ninth century, its kings must have long given up hope of returning to the big league.